Researchers are very interested in figuring out how memory works, as well as what consciousness is. In order to gather more insight into these areas, they are studying the phenomenon of lucid dreaming in which people are aware, within a dream, that they are within a dream. Lucid dreaming can be accompanied by the ability to alter the dreaming environment at will.
I'm not yet one of the people who can control how often they have lucid dreams, yet last night I had one. After the initial testing to check if it was indeed a dream (poking a hard surface and seeing it bend around my finger), and the inevitable playing out of certain "quick scenarios that could not happen in real life" (leave that to the imagination), I proceeded to do a few in-dream experiments.
I tried to see just how much I can alter within the dream, and what the limitations are.
1. After continuously altering everything in the environment for a few seconds, it became too difficult to continue. I got fatigued and changing things because more difficult.
2. Arbitrary elements persisted in the environment unless I specifically removed them - i.e. there is a stock background. It is easier to put things in than isolate them and take them out.
3. Just like in The Matrix, you have to believe in what you are attempting to create. If you doubt yourself it takes longer to change a chair for example into an armchair.
Pending question: are the experiences perceived in dreams purely replicas of experiences already lived, or can they be generated anew, and therefore stay unique to the dream world?